A new anatomical link between the brain and the immune system which may provide greater understanding of disorders of the nervous system has been revealed recently. Kevin Lee, chairman of the University Of Virginia School Of Medicine’s Department of Neuroscience, remembers his initial response: “they’ll have to change the textbooks”.
The lab of Jonathan Kipnis, director of the UVA’s centre for Brain Immunology and Glia (BIG), published their finding lymphatic vessels draining the brain in dissections of mice and human tissues, and confirmed with live imaging. Traditionally the brain was considered to have no lymphatic drainage, and although it was acknowledged that immunological monitoring took place, there was no clear mechanism to explain the passage of immune cells in and out of the central nervous system.
However, these vessels have been found lining dural sinuses (which drain internal and external veins of the brain into internal jugular veins) – blood vessels may have delayed this discovery until a new technique was used. Kipnis’ lab fixed tissue before dissection to reveal the whole structure on a single slide for examination – a combination of molecular, structural and functional characterisation indicates they are in fact functional lymphatic vessels.
The discovery of these vessels poses questions about their involvement in neurological disorders such as autism and Alzheimer’s disease. Kipnis proposes that Alzheimer’s characteristic accumulation of dysfunctional protein may be due to inefficient drainage by these vessels, which may be supported by evidence that they change with age as it is a disease associated with older people. The missing link between immune and nervous systems may shed light on the development and potentially treatment of other disorders: malfunctional lymphatic drainage could be causing neurological disorders with altered immunity, for example multiple sclerosis.